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# AQA Physics PHYA4 - 20th June 2016 [Exam Discussion Thread] watch

1. (Original post by McDerdactyl)
Is anyone else completely screwed? Ive tried a few past papers today and couldnt even do half... I couldnt bring myself to grade them :/
Grade boundaries are very low, so don't feel discouraged if you have to skip parts
2. (Original post by kingaaran)
I'm guessing a 6 marker on SHM is due... Probably something to do with damping / resonance or a calculation based one
Would be nice but there was a damping and resonance based explain question (4 marks) last year (cone with ring) so may decrease the chance?
3. (Original post by nav1234567)
Are you sure it's not when they are perpendicular to the field? Induced emf is directly proportional to rate of change of mag flux linkage
Emf is maximum when the flux linkage for the coil is zero. Mind you flux linkage and rate of change of flux linkage are two very different thing
The RATE of change of flux linkage is max when the coils are parallel with the field lines
Is the rate of change of flux linkage NΔΦ/Δt. And NΦ=BANcos(theta) so when theta is equal to 90 it gives 0 for NΦ.
Ergh these two formulas keep annoying me...
5. (Original post by Music With Rocks)
Grade boundaries are very low, so don't feel discouraged if you have to skip parts
How do you know they're really low? I know most of the stuff, its just the application. The wording of the questions completely puts me off even though I look at the mark scheme and I actually knew it...
6. PEOPLE

With a coil rotating in a magnetic field, the flux LINKAGE is maximum when the plane of the coil is parallel to the field lines. However the rate of change of flux linkage (which is proportional to the induced emf) is maximum when the plane of the coil is perpendicular to the field lines! Hope this clears some confusion

This can be seen as flux linkage is related to cos. cos(0)=1 i.e. maximum when parallel
emf is related to sin. sin(90)=1 i.e. maximum when perpendicular
7. In an radial electric field does the field strengh get bigger when you move closer to the charge causing the field?
8. In calculations do you carry all the decimal places in your calculator - I've done this sometimes and sometimes it give the right answer and other times I'm a decimal place out. Also if it says show that do you use the answer you've been given or your answer to more sig figs
The RATE of change of flux linkage is max when the coils are parallel with the field lines
(Original post by nav1234567)
Are you sure it's not when they are perpendicular to the field? Induced emf is directly proportional to rate of change of mag flux linkage
I am not sure if your wording is just confusing me but it is when the coil face is perpendicular to the magnetic field.

EDIT: sorry did not see that you were talking about rate
10. (Original post by mohdstudent)
9.81 it is in the formula book.
oh right, of course
11. (Original post by Music With Rocks)
Would be nice but there was a damping and resonance based explain question (4 marks) last year (cone with ring) so may decrease the chance?
But they can ask about that graph - amplitude vs frequency - or something. Idk we'll see, just a guess
12. (Original post by Music With Rocks)
I am not sure if your wording is just confusing me but it is when the coil face is perpendicular to the magnetic field.

EDIT: sorry did not see that you were talking about rate
Yes I meant coil face, if you think about it the coils(wires) can never be parallel to the field lines, so what's there to be confused about? :P
13. (Original post by McDerdactyl)
How do you know they're really low? I know most of the stuff, its just the application. The wording of the questions completely puts me off even though I look at the mark scheme and I actually knew it...
Looking at all the boundaries from previous years, they are highly unlikely to drastically change
14. (Original post by duncant)
I think B is correct. A is wrong because emf is only induced when it CUTS field lines, e.g. when it is perpendicular to the field. So it is actually 0 here. note: magnetic flux linkage through the coil is maximum when parallel to the field lines, as there are max. number of field lines going through the coil.
So when the coil is parallel to the field, the emf is 0 but flux linkage max?
15. (Original post by Music With Rocks)
Looking at all the boundaries from previous years, they are highly unlikely to drastically change
Ive got them on my wall so I need just under half marks for an E by the looks of those which I can hopefully do... I just don't want a U I'll take an E ahahah
16. (Original post by boyyo)
So when the coil is parallel to the field, the emf is 0 but flux linkage max?
Emf is zero when the coil is perpendicular to the field. Flux linkage is max when emf is 0
17. (Original post by abro1089)
PEOPLE

With a coil rotating in a magnetic field, the flux LINKAGE is maximum when the plane of the coil is parallel to the field lines. However the rate of change of flux linkage (which is proportional to the induced emf) is maximum when the plane of the coil is perpendicular to the field lines! Hope this clears some confusion

This can be seen as flux linkage is related to cos. cos(0)=1 i.e. maximum when parallel
emf is related to sin. sin(90)=1 i.e. maximum when perpendicular
The RATE of change of flux linkage is max when the coils are parallel with the field lines
Which one is right?
18. (Original post by TajwarC)
Emf is zero when the coil is perpendicular to the field. Flux linkage is max when emf is 0
Look at the two I quoted, everyone is saying different things :/.

19. (Original post by particlestudent)
Look at the two I quoted, everyone is saying different things :/.
20. The alternating current generator:

You have the greatest emf induced when the sides of your coil are perpendicular to the field lines. This is where the rate of change of flux linkage is largest, generating the maximum emf.

You have the smallest emf when the sides of your coil are parallel to the field lines. This is where the rate of change of flux linkage is least, generating the lowest emf (which is, in fact, 0).

People on here seem to be getting confused between the sides of the coil and the plane of the coil.

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